Power supply circuit



i Jan. 29, 1963 R. P. FARNswoRTH ETAL 3,076,135

POWER SUPPLY CIRCUIT Filed Sept. 29, 1958 En NM 3,tl76,i35 PGV/liliSillery? Cil-mill? Rohert i. Farnsworth, Los Angeles, and Leonard Azar,

#Culver City, talil., assignors to Hughes Aircraft Cornpany, GCulverCity, Cali, a corporation ot Delaware Filed Sept. 2.9, 1953, der. No.765,693

1l Claims. (Qi. 323-22) This invention relates to power supplies andparticularly to a direct-current power supply utilizing a fast actingoverload protection circuit.

ln the prior art, DC. (direct current) power supplies were used inconnection with vacuum tubes and delivered relatively high outputvoltages and could operate with relatively high output impedances.However, with transistor circuitry, power supplies may be required tosupply relatively low output voltages while supplying current of 25amperes or more. The output impedance of the power supply may berequired to be less than l"3 ohms. These problems have been solved byutilizing power supplies with high power transistors for regulation andlow forward resistance diodes for rectiiication.

he low output impedance from these power supplies has created newproblems, the most formidable one being that of protecting the powersupply and the load against short-circuits or accidental overloads.During a shortcircuit or accidental overload condition, destruction of.the transistors and rectiiiers of the power supply as well asdestruction of the transistor circuitry being supplied with power occursat a fast rate. The time required for destruction may be in the order of100 microseconds under severe conditions. Conventional fuses ormechanical disconnections require 2G to 30 milliseconds to open, whichoperation is far too slow to protect transistors. Some electronicdisconnect circuitry of the prior art samples signal current in aregulator loop and provide turmoil of the supply when the signal currentreaches a preset value. The .shortcoming of this system is that thesignal current is related to the load current by the gain of one or morestages of the supply, which gain is dependent upon ageing andtemperature oi the circuit elements, as well as upon supply voltages.Thus, the turn-oft current is variable and changes under theseconditions so as to not consistently disconnect the power supply at axed maximum load current.

Also, some conventional power supplies having automatic turn-oitcharacteristics follow a turn-oit path which a though allowing them toturn on under full load ater removal of a short circuit condition, willalso allow them to exceed maximum dissipations under partial shortcircuit. Other conventional power supplies follow a path which allowsthem to turn completely off when an overload condition occurs under fullload but requires partial removal of the full load to turn on after theoverload or short circuit condition has been corrected. rhese turnon andturn-od characteristics may result from the nonlinearities of the systemcomponents. A system which would provide tast operating overloadprotection, that would provide overload protection at a fixed maximumload current independent oi the gain of the circuit elements, and whichwould turn both completely oli and completely on when a short circuitcondition occurs and is removed at full load, would have wide use,especially with transistor circuitry.

lt is, therefore, an object of this invention to provide a power supplywhich rapidly disconnects from its load upon the occurrence ot a shortcircuit or an overload condition.

it is a further object of this invention to provide a transistor powersupply which turns ott under an overload condition and turns on uponremoval of the overload condition at a consistent maximum load currentvalue,

3,dlli,l35

Datenteel dan. 29, lgi

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ad independent of temperature and ageing of the amplifying elements inthe circuit.

It is a still further object of this invention to provide a fast actingpower supply utilizing transistors which will not only completelydisconnect the source from the load during an overload condition whenoperating at full rated power but will return to supplying full ratedpower upon removal of the overload condition.

Another object of this invention is to provide a transistor power supplyhaving a simplified overload protection circuit for protecting both thepower supply and the supplied circuitry, and which operates todisconnect the power supply at a predetermined rated current independentof changes of characteristics of the transistor due to ageing andtemperature.

According to one feature of this invention, a power supply receivesunregulated direct current voltage from a transformer and rectifierarrangement, and supplies it to a load through a series connectedregulating, or control, transistor which varies in static impedance inresponse to changes of its base current. A voltage comparator includinga i'lrst diilerential aniplier and a voltage divider both connectedacross the load, is utilized to control a current signal in response tochanges in the load voltage or potential diiierence. A seconddifferential amplier is connected to the base of the control transistorand is connected to the lirst differential amplifier for responding tothe changes of the current signal to maintain the constant load voltage.An overload control circuit is provided including a resistor connectedfrom a terminal of the control transistor and in series with the load toform a rst voltage divider and including a second voltage dividerconnected from the same terminal of the control transistor to the otherside oi the load. A signal-forming transistor is connected between therst and the second voltage dividers so as to respond to a predeterminedpolarity of potential dilierence indicating maximum rated load. Thesignal forming transistor is connected to shunt out the current from thetirst differential amplilier in response to the predetermined polaritywhich in turn biases the regulating transistor out of conduction toetectively disconnect the source from the load. A leakage path acrossthe control transistor maintains this disconnected condition bysupplying a small current through the first and second voltage dividers.When the overload condition is removed the potential difference betweenthe lirst and second voltage dividers returns to a polarity to bias thesignal-forming transistor out oi conduction, thus allowing the voltagecomparator circuit to continue its regulating operation at any load upto maximum load.

The novel features of this invention, as well as the invention itself,both as to its organization and method of operation, will best beunderstood from the accompanying description, taken in connection withthe accompanying drawings, in which:

PIG. l is a schematic diagram of the power supply circuit of thisinvention; and

FlG. 2 is a graph to illustrate the operation of the circuit of FIG. l.

Referring iirst to FIG. l, a schematic circuit diagram is shown of thepower supply circuit including the overload protection arrangement ofthis invention. The power supply of this invention receives unregulatedvoltage, which may be -32 volts, from an unregulated voltage source 2@comprising a transformer and alternating current voltage source 22connected to a terminal 2S which may be at ground potential and arectitler 2d connected to the transformer and voltage source 22. riheunregulated voltage source Ztl supplies power through a regulatingtransistor 26 of a regulating element circuit 32. to a load 34, whichmay include a resistor RL, and is connected to the terminal 25 through aground lead lith. The regulating element circuit 32 also includes adriver transistor 38. The regulating transistor 26 which may be of thePNP type has a base 46, an emitter 42 and a collector 4t), and thedriver transistor 318 which may be of the NPN type has a base Sti, anemitter 4S, and a collector 46. The collector ttl of the regulatingtransistor 26 is connected to the rectifier 24 and the base de of theregulating transistor 26 is connected to the collector i6 of the drivertransistor 33. The emitter d8 of the driver transistor 33 is connectedto the collector itl of the regulating transistor 26 to provide a returnpath for current from the base 44 of the regulating transistor 26, aswill be explained subsequently. A leakage resistor 54 is connectedbetween the collector d@ and the emitter t2 of the regulating transistor26 and, as will be explained hereinafter, passes a current to maintainthe circuit disconnected during an overload condition.

The base 56 of the driver transistor 38 is connected to acurrent-amplifier circuit 6d which utilizes a differential amplifier iorcontrolling the current passed into the base Sil of the drivertransistor 38. The diiferential amplifier includes a transistor 64 and atransistor 66 both of which may be of the PNP type. The transistor 64has a base 66, an emitter 7d, and a collector 72, and the transistor 66has a base 74, an emitter 76, and a collector '76. The collector 72 ofthe transistor 64 is connected to the base t! of the transistor 36 andthe collector 7S of the transistor 66 is connected to the collector 46of the regulating transistor 26. A biasing resistor Si) is connectedbetween the collector 72 of the transistor 64 and the collector 78 ofthe transistor 66 to provide a leakage current path from the base Sil ofthe transistor 38 when the transistor 38 is biased out of conduction, aswill be explained subsequently. The emitters 70 and 76 of thetransistors 64 and 66 are connected by way of a currentlimiting resistor32 to a lead 84. The lead 3d is conected to a terminal 88 which may beconnected to a |l5 voltage unregulated source (not shown), whichprovides a bias for maintaining operation of the circuit during anoverload condition. The base 68 of the transistor 64 is connected to alead 99 and the base 74 of the transistor 66 is connected to a lead 92through which leads, control current passes, as will be explainedsubsequently. Thus, the current ampliiier circuit 66 is connected forcontrolling the regulating element circuit 32.

The current amplier circuit 6i) is controlled by an overload controlcircuit 94 and a voltage comparator circuit 96. The overload controlcircuit 94 includes a resistor R1 having one end connected to a junction100 which, in turn, is connected to the emitter d2 of the regulatingtransistor 26. The other end of the resistor R1 is connected through alead 162 to the resistor RL of the load 34. The load current lL isindicated by an arrow 101. The resistor R1 in combination with theresistor RL of the load 313i provides a first voltage divider, as willbe explained subsequently. The junction 100 is also connected through alead 103 to a resistor R2 which in turn is connected to one end of aresistor R3 by Way of a lead 166. r[he other end of the resistor R3 isconnected to the ground lead 168. The lead 102 is connected to thecathode of a diode 112 which has its anode connected to one end of aresistor 114 by lead 116. The other end of the resistor 114 is connectedto the lead 84.

A signal transistor 117 which may be of the NPN type has a base 118, anemitter 126, and a collector 122 with the base 118 connected to the lead116 and the emitter 126 connected to the lead 106. As will be explainedsubsequently, the difference in potential drop across the resistor R1and the diode, 112 and across the Aresistor R2, which potentialdifference appears betweenthe leads 116 and 166, determines whethertransistor 117 is biased into conduction. rlhe collector 122 of thetransistor 117 is connected to the base 126 of a transistor 124. whichmay be of the PNP type. I The transistor 124 has an emitter 128 which isconnected to the lead 84 and has a collector 130 which is connected tothe lead 9@ at a junction 132. Thus, it can be seen that current passesinto the junction 132 either from the transistor 12tor from thetransistor 64 of the current amplifier circuit 66. The lead 103 is alsoconnected to the base le of the regulating transistor 26 by'way of abiasing resistor 136 which acts to pass leakage current from the base 44to maintain the regulating transistor 26 biased when in itsnonconducting state, as will be explained subsequently.

The voltage comparator circuit 96 includes transistors 138 and 146yarranged as a second differential amplifier circuit. The transistors1355 and 146 may be of the PNP type. The transistor 138 has a base 14),an emitter 162, and a collector 144, and the transistor 166 has a base146, and emitter 156, and a collector 152. The collector 144 of thetransistor 138 is connected to the lead 162 by way of a biasing resistor156 and the collector 152 of the transistor 146 is connected to the lead102 by way of a biasing resistor 158. The emitters 142 and 150 of thetransistors 138 and 146 are connected to ground lead 108 by way of acurrent limiting resistor 159. The base 148 of the transistor 146 isconnected to a lead 162 by way of an impedance-matching resistor 16d.The lead 162 is connected to the ground lead 106 by way of a resistor166 and is connected to the cathode of a diode 168, which may be a Zenertype diode. The anode of the diode 168 is connected to the lead 102 toprovide a potential to the base 14S of the transistor 146 which followsthe variation ot' the load potential on the lead 102. It is to be notedthat the resistor 164 is utilized to match the impedance out of the base14S of the transistor 146 to the impedance out of the base 1d@ of thetransistor 136.

The base 146 of the transistor 13S is connected by a variable tap 172 toa resistor 174, one end of which is connected to the lead 102 by way ofa resistor 176 and the other end of which is connected to ground lead168 by way of a resistor 178. The resistors 174, 176, and

178 thus are a voltage divider of the potential dierence -acrossthe load34 for dividing out a potential to control the conduction of thetransistor 138. The collector 144 of the transistor 138 is connected tothe lead 92 which,

` in turn controls the conduction of the transistor 66, as

will be explained subsequently. The collector 152 of they transistor 146is connected to a lead 182 which, in turn is connected to the junction132 for receiivng current from either the transistor 64 during normalregulation or from the transistor 124 during an overload condition, aswill also be explained subsequently. A capacitor 180 is coupled acrossthe leads 102 and 166 to stabilize the circuit for providing a lowoutput impedance to signals on the lead 102 at a frequency above thefrequency response of the transistors. in the circuit, as is well knownin the art.

The operation of the voltage regulator of this invention includes bothnormal voltage regulation of the load voltage on the lead 102 tomaintain a regulated voltage and overload protection during operationwhen, for example, a fault such as a short circuit of the load 34occurs. During normal regulation, the regulating circuit controls thecurrent through the series element which is the transistor 26, tocorrect variations of the regulated potential on the lead 102 causedeither by voltage fluctuations of the source 2t) or by small variationsof the effective resistance of the load 3.4. A rise of potential on thecollector 40 from a positive-goingfluctuation of the unregulatedpotential from source 26` decreases the emitter torcollector potentialof the regulating transistor 26 and atgthe value of the currentdetermined by the potential on the b-ase 44, results in a small decreasein collector current. This decrease oi collector current is accompaniedby a decrease of the current passing through load RL, which results in arise in potential on the lead 102. This rise in potential is sensed bythev voltage comparator circuit 96 and, as will be described, acts tolower the potential on base liti. This condition decreases the staticimpedance of the transistor 23.6 to slightly increase the load currentso as to increase the potential drop across the resistor RL and torestore the regulated potential on the lead 162.

A decrease of the effective value of the resistor RL also causes anincrease of potential on the lead i162. lt is to be noted that thiscondition causes only a small increase of collector current of theregulating transistor Z6 as determine by the potential on the base da.The increase of potential on the lead Teil2 is sensed by the voltagecomparator circuit 9o and, as will be described, acts to lower thepotential on the base i4 of the regulating transistor 26 so as todecrease the static impedance of the transistor 26 and to increase thecurrent from emitter 42 to collector tu a required amount. rthisincrease of collector current increases the current passing through theload RL and causes a fall in potential on the lead lilZ, thus restoringthe regulated potential on the lead lZ.

The operation of the voltage comparator' circuit 96 and the currentamplifier circuit oli during norrnal voltage regulation will now bedescribed. During normal voltage regulation, the transistor il? isbiased out of conduction to interrupt the current path through thetransistor 124 to the junction 132. Thus, the potential developed on thecollector 152 of the transistor 146 from current passing through thetransistor ldd and the resistor 158 is impressed through the lead lil?!to the base ed to control conduction of the transistor ed. An increase(positivegoing) of potential at the base ldd oi the transistor M6 fromthe lead lo?. results in a decrease of potential on the collector 152 ofthe transistor ido. This decrease (negative-going) of potential isimpressed on the base 68 to increase the conduction of the transistor64, and to increase the potential on the base Sil of the transistorTail. The transistor 33 is thus biased into further conduction and thepotential on the hase of the transistor 26 is decreased to increase theernitter to collector current through the transistor 26.

The potential impressed on the base ldd ot the transistor i353 is alsodetermined by the load potential on the lead im, which potential acts toVary the current passed from the emitter i142 to the collector ldd ofthe transistor T138. An increase of potential on the base l-i results inan increase of potential on the collector les? of the transistor i3dbecause of the differential ampliiier action, as will be described,which potential is impressed on the base 74 of the transistor od todecrease its conduction. rlfhus, the potentials on the collectors ltd-4land i152 are impressed through the leads 92 and i182 to the bases 7d and68 oi the transistors 6d and ed.

The differential amplifier arrangement is utilized so that changes ofgain characteristics of the transistors ed, 66, i3d and lele have a verysinall eiiect on the regulating action. A. substantially constantcurrent passes through the current limiting resistor 59 and through theparallel resistors iSv-i and ldd. Thus, changes of the gaincharacteristics due to ageing or temperature changes, for example, ofthe transistors i3d and M6 has a relatively small eiiect on thedifference in potential on the collectors las and 152. The difference inpotential on the leads 92 and ld?. is the value which controls theamount of conduction of the transistors 66 and ed and, in turn, theimpedance oi the regulating transistor Zd. The current-limiting resistord2 passing a constant current into the transistors 64 and ed of theiirst difierential ampliier circuit, cancels changes oi gaincharacteristics of the transistors 6d and on in a similar manner.rl`hus, the differential amplilier arrangements of transistors i353,145, 64 and do is utilized to provide reliable regulation independent oftemperature changes or ageing of the transistors, for example.

During the regulating operation of the power supply,

the potential on the lead luz is regulated to -25 volts by the action ofa servo loop including a voltage cornparator 96 and the path to the oasela of the regulating transistor 2o. An increase of potential on the leadle?. resulting from a Voltage variation ot the source 2d or a srnalldecrease in the value of the load 3ft impedance, as discussed, impressesthe increase of potential through the constant voltage Zener diode lodto develop across the resistor lo for application to the 'oase 14S ofthe transistor lido, as a potential increase substantially similar inamplitude to the increase on the lead lilZ. The transistor 146 is thusbiased so as to decrease its conduction and this decreased current iiowthrough the resistor 153 results in a decrease of the potential on thecollector lSZ, which decrease is impressed on the base 65 of thetransistor 64 to increase its conduction. At the same time, a smallincrease of potential is impressed on the base lati of the transistor13S from the tap 172. However, because of the large decrease or" currentthrough the transistor ldd and through the resistor ld, the currentpassing through the transistor 133 is increased. This increase ofcurrent results from the diiierential action of a constant currentpassing through the current limiting resistor l59. Thus, there is anincrease of potential on the collector lll-4iof the transistor 13S whichis impressed on the oase 711i of the transistor do to bias it furtherout of conduction. As a result of this action, the potential on thecollector '.72 of the transistor ed is increased because of the decreaseof potential on the base eff; to bias the transistor 38 into furtherconduction and to decrease the potential on the base or" the transistor'26. in response to tne decrease of potential on the base 4d, the staticimpedance of the transistor 25 is decreased and increased current passesthrough the load RL to decrease the potential on the lead so as tocorrect the original rise in potentie. lt is to be noted that thisoperation is continuous. Also, a potential decrease on the lead lo?. iscorrected in a similar but opposite manner.

New that the norrnal regulating action of the power supply has beenexplained, the action of the overload control circuit 9d resulting froman overload condition such as a short circuit of the load 34, will bedescribe rthe ratio oi the value of resistor R1 to that of the resistorRL of the load to the ratio o the value of resistor R2 to that of theresistor R3 is the relation which determines the condition when anoverload condition, such as a short circuit, or" the load 3d is present.it is to oe noted that a short circuit of the load 34 results in theresistance RL being effectively reduced in value and a current il,larger than rated current being supplied. The transistor fir? is biasedout of conduction during the normal regulating action when the voltagedrop across the resistor R1 is less than the voltage drop across theresistor However, when the voltage drop across the resistor R1 isgreater than the voltage drop across the resistor R2, resulting from aniaximurn load current passing through the resistor R1 and the junctionlilo, the transistor ll is biased into conduction. Under theseconditions, the ratio of R1 to RL is greater than the ratio of R2 to R3indicating a decrease of the eiiective value ot the load resistor R Theminimum effective load resistance lmmm) is equal to Titus, tl e maximumcurrent if (mx) which is equal to 7, is the regulated voltage fordetermining the maximum load current at which the overload controlcircuit 9d becomes operative. When the load current IL increases abovethe maximum rated value so that the voltage drop across the resistor R1is greater than the voltage drop across R2, the transistor 117 is biasedinto full conduction. Thus, the transistor 124 is biased intoconduction, passing current from the emitter 12S to the coilector 13@and into the junction 132 and to the lead 132. The positive potentialfrom the lead 34 is impressed through the transistor 124iand upon thebase d8 of the transistor de to bias it out of conduction. When thetransistor 64 is biased out of conduction, the driver transistor 3S isbiased out of conduction and, in turn, the regulating transistor 26 isbiased out of conduction to develop a high impedance to flow of loadcurrent IL. Thus, the source 20 is effectively disconnected from theload 34 under this overload condition.

The foregoing overload condition with the transistor 3.1"/ biased in aconductive state is maintained by a small current flow through theleakage resistor ft or by a small leakage current through the transistor2d. it is to be noted that when the transistor Zd is of a type with asmall leakage current, the leakage resistor 5d is not required. Thisleakage current passes from the resistor RL through the resistor R1 aswell as through the resistors R3 and R2 to the junction litt) tomaintain a potential ditterence from the base 118 to the emitter i2@ ofthe signal transistor li?. The potential drop across the resistor R2 isgreater than the drop across the resistor R2 because of their relativevalues. The base lid of the transistor 1l? is biased by current passingfrom the +15 volt unregulated source at the terminal 88 through theresistor i114, through the diode M2 and through the leakage resistor 5d.It is to be noted that current through the resistor 1M acts to maintainthe diode H2 forward biased during both normal regulation and anoverload condition. Also, the transistor i24- is biased into conductionduring an overload condition by the +15 volt potential from the terminal3S to apply the biasing potential to the junction 32 and the base 68 ofthe transistor Thus, the +15 volt terminal dit is required to maintainthe transistors T17 and 124 biased in conduction during an overloadcondition.

The transistor lll' and the diode i12 are of similar type materials, sothat an increase in impedance characteristics of the diode 112 and thetransistor lill from temperature changes, for example, is similar. Thus,an increase of impedance characteristics resulting in an increasedpotential diiTerence for biasing the transistor M7 into conduction iscancelled by an increase of potential drop across the diode 112.Thererore, the ratio of potential drop across the resistors R1 and R2for biasing the transister M7 into conduction remains constant and themaximum load current lL at which the overload protection circuit becomesoperative remains constant.

'When the load 34 returns to a condition such that there is a voltagedrop across resistor RL indicating a required load current of maximumload current or less to cause a decreased voltage En to be impressed onthe lead Th2, the potential drop across resistor R1 will be less thanthe potential drop across the resistor R2. Thus, the tran sistor lil? isbiased out of conduction, the transistor 124 is biased out ofconduction, and the transistor d-iis biased into conduction to cause thetransistors 38 and 26 to be biased into conduction. Thus, the normalregulating action of the voltage comparator circuit 96, as previouslydescribed, 'will continue.

While it will be understood that the circuit specification of the powersupply of the invention may vary according to the design of anyparticular application, the following circuit speciications for a powersupply are included, by way of example only, suitable to supply aregulated voltage ofA -25 volts at a maximum load cur" 8 rent of lampere to a grounded load from a -32 volt unregulated source:

Transistor 2d, Delco (GM) 2N173 Transistor 3S, Sylvania 2Nl42 Transistorde, General Electric 2N123 Transistor de, General Electric 2N123Transistor lli?, General Electric 4jD4A5 Transistor 121i, Philco T 1275Transistor i3d, Hughes HA-7550 Transisto-r'ild, Hughes IHA-7550 Terminald8 volts +15 Resistor ohms 2,000 Resistor dit do 10o Resistor 82 d0-`10,000 Resistor i312 do l0 Resistor R1 do 2 Resistor R2 do 909 ResistorR3 do 11,300 Resistor Rmmm) do 25 Resistor il@ do 39,009 Resistor 156 d05,110 Resistor 153 do 5,110 Resistor 159 -do 8,060 Resistor 16tdo 560Resistor lied do-.. 1,690 Resistor 174 do 200 Resistor 176 do 75()Resistor 17S do 1,580 Capacitor ld@ microfarads 350 Diode i12, Hughes6,007 .Diode 168, Hoffman iN 430A lt is to be noted that although thepower supply has been described as supplying negative potentialsrelative to ground potential, it may be easily arranged to supplypositive potential relative to ground potential by reversing allvoltages and changing the transistor types.

Referring now to FIG. 2, which is a graph of load potential versus loadcurrent, as well as referring to FiG. l, the operation of the voltageregulator will be explained in further detail. The constant regulatordissipation line 184i is shown to indicate the power capabilities of theregulating transistor 26. The regulated potential is shown as -25 volts,and the maximum load current is shown as 1 ampere which is equal to EuRzRlRa En E of the turn-ofi line may be expressed by the followingrelation when the transistor 117 is biased into conduction upon theoccurrence of an overload condition:

IL- R2 Thus, the return path of the load current and the load voltage isdetermined only by the values of the resistors R1, R2 and R3 in the twovoltage divider circuits. i This linear turn-on' curve ide allows thevoltage regulator to turn completely oli when an overload condition atmaximum load current occurs and to turn completely on to supply maximumload upon removal or" the overload condition. The operation of thecircuit when turning on to supply a load which is less than maximum isshown by a line ttl. lt isA to be noted that conventional voltageadsense impedance element and a load connected between terminals of saidsource, a comparator loop coupled in parallel with said load fordeveloping a signal proportional to minor variations in Voltage acrosssaid load and means for connecting said proportional signal to a controlterminal of said variable impedance element to overcome said minorvariations when said loop is operative, comprising first impedance meanscoupled between said variable impedance element and said load fordeveloping a iirst potential, second impedance means coupled from oneside of said load at a point between said Variable impedance element andsaid iirst impedance means to the opposite side of said load fordeveloping a second potential proportional to the voltage across saidload, and switching means coupled from between said first imp-edancemeans and said load to said second impedance means to be renderedconductive or nonconductive in response to the dierence in potential ofsaid first and second potentials across said first and second impedancemeans and including means coupled to said comparator loop for applyingkan overload signal to bias said switching means into conduction forcontrolling said comparator loop to be inoperative and to increase theimpedance of said impedance element to disconnect said source from saidload when said current through said load exceeds a predetermined value.

6. A regulator circuit comprising an unregulated voltage source havingfirst and second terminal, a series circuit including in relative ordera variable impedance coupled to said first terminal, a iixed impedanceand a load coupled to said second terminal, means connected in parallelwith said load including a differential amplifier to develop aproportional signal in response to minor variations of potential acrosssaid load and including means for coupling said proportional signal to acontrol terminal of said variable impedance to overcome said minorvariations, voltage divider means coupled from between said variableimpedance and said iixed impedance to said second terminal, switchingmeans having either a first state of conduction or a second state ofnonconduction and coupled from between said fixed impedance and saidload to said voltage divider means to be responsive to the difference inpotential across said fixed impedance and said load and across saidvoltage divider means to supp-ly a disconnecting signal to said variableimpedance when current through said load exceeds a predetermined Valueto bias said switching means to said rst state, and a leakage pathacross said variable impedance for conducting a current to maintain saiddisconnecting signal while said load is in a condition to pass a currentwhich exceeds said predetermined value.

7. A voltage regulator comprising an unregulated source, a seriescircuit including a regulating element and a load coupled betweenterminals of said source, a feedback loopl coupled to develop a signalproportional to variations of potential across said load and includingamplifying means for coupling said proportional signal to a controlterminal of said regulating element, a first impedance means coupledbetween said regulating element and said load for forming a firstVoltage divider with said load, a second voltage divider coupled frombetween said regulating element and said rst voltage divider across saidload, overload means having a rst state where said overload means isconductive and a second state where said overloadV means isnonconductive and coupled to said irst and second voltage dividers to beresponsive to the diderence in potential between said first and secondvoltage dividers for developing a disconnecting signal for increasingthe impedance of said regulating element to disconnect said source fromsaid load when current through said load exceeds a maximum value andsaid overload means is biased to said first state, a current leakagepath coupled in parallel to said regulating element for passing acurrent through said first and second voltage dividers to maintain saiddifference in potential i2 when said regulating element is disconnected,and a source oi biasing potential coupled to said overload means forbiasing said overload means to maintain said disconnecting signal whensaid load is in a condition to pass current which exceeds said maximumvalue.

A voltage regulator circuit for supplying current from an unregulatedsource through a load, comprising regulating means controlled to vary inimpedance to load current coupled between one terminal of said sourceand said load and having a control terminal, voltage comparing meansincluding a rst differential amplier con nected to develop a signalproportional to minor variations of potential across said load andincluding a second differential amplifier connected to said controlterminal for responding to said proportional signal to control saidregulating means for correcting said minor variations, iirst voltagedividing means coupled between said regulating means and said load,second voltage dividing means coupled from one side of said load at apoint between said regulating means and said first voltage dividingmeans to the other side of said load and responsive to the voltagedeveloped across said load, overload means controllable to be biasedinto a first state of conduction or into a second state of nonconductinand coupled between said first and second voltage dividing meansresponsive to a potential difference having a polarity indicative of amaximum load current for being biased to said iirst state to apply anoverload signal to said second dilierential amplifier for disconnectingsaid regulating means, a current leakage path coupled in parallel withsaid regulating element to conduct current for maintaining saidpotential difference when said regulating element is disconnected, and asource of biasing potential for biasing said overload means to maintainsaid overload signal when said polarity is indicative of said maximumload current.

9. A regulator circuit to supply current at a constant potential from anunregulated source through a load coupled between terminals of saidsource and comprising a regulating transistor having anemitter-collector path coupled between said source and said load andhaving a base, an impedance coupled between said ernitter-collector pathand said load to form a first voltage divider with said load, a secondvoltage divider coupled from between said regulating transistor and saidimpedance across said load for responding to variations of potentialacross said load, a comparator circuit including a first differentialamplifier coupled across said load for developing a signal proportionalto variations of potential across said load, a source of maintainingpotential, a second diferential amplifier coupled between said base ofsaid regulating transistor and said source of maintaining potential andconnected to respond to said proportional signal for controlling theimpedance of said regulating transistor to correct said variations ofpotential, a first overload tran sistor having a base coupled to saidiirst voltage divider and having an emitter-collector path coupled tosaid second voltage divider, a second overload transistor having a basecoupled to the emitter-collector path of said first overload transistorand having an emitter-collector path coupled between said source ofmaintaining potential and said second differential amplifier to overcomesaid proportional signal and disconnect said regulating transistor whensaid first overload transistor is biased into conduction in response toa predetermined polarity of a potential difference between said firstand second voltage dividers indicative of a greater than maximum loadcurrent, and a leakage path across said emitter-collector path of saidregulating transistor for passing current through said first and secondvoltage dividers to maintain said potential diierence when said polarityis indicative that greater than maximum current would pass through saidload.

10. A power supply circuit to provide load current at a constantpotential from an unregulated source to a load and to disconnect saidsource from said load during an overload condition when said loadcurrentexceeds a predetermined value, comprising a regulating transistorhaving a load current path coupled between said source and said load andhaving a base terminal, signal amplitier means coupled to said baseterminal for controlling the impedance of said regulating transistor andhaving a control terminal, a voltage comparator coupled across said loadto respond to potential variations and coupled to said control terminalof said amplilier means for correcting said potential variations, aiirst resistor coupled be tween said load current path of saidregulating transistor and said load for forming a first voltage dividerwith said load, a second voltage divider coupled from one side of saidload at a point between said load current path of said regulatingelement and said lirst resistor to the other side of said load forresponding to the potential across said load, a tirst signal formingtransistor having a base coupled to said tirst voltage divider andhaving an emittercollector path coupled to said second voltage divider,a second signal forming transistor coupled between saidemitter-collector path of said first signal fortning transistor and saidamplifier means and being biased into conduction for developing anoverload signal in response to a predetermined polarity of potentialbetween said first and second voltage dividers for biasing said iirstsignal forming transistor into conduction indicative of an overloadcondition causing said load current to exceed said predetermined value,said overload signal acting to increase the impedance of said regulatingelement to decrease said load current to a maintaining current having asmall value relative to said predetermined value, said maintainingcurrent passing through said first and second voltage dividers tomaintain said overload signal for disconnecting said source from saidload during the occurrence of said overload condition.

11. A circuit connected between the positive and negative terminals ofan unregulated source to supply current through a load at a constantpotential, comprising a regulating transistor having anemitter-collector path coupled between said negative terminal of saidsource and said load and having a base terminal, a resistor coupledbetween said regulating transistor and said load to form a first voltagedivider with said load, a second voltage divider coupled between saidregulating transistor and said resistor to said positive terminal fordeveloping a potential proportional to the potential developed acrosssaid load, a comparator loop including a irst diiierential arnpliiiercoupled to develop a signal proportional to the potential variationacross said load and including a second differential amplifier coupledbetween said base terminal and a source of biasing potential beingpositive rela. tive to said positive terminal of said source forresponding to said proportional signal developed by said comparator loopto vary the impedance of said regulating transistor for correcting saidpotential variation, a first control tran. sistor having a base coupledto said first voltage divider and to said source of biasing potentialand having an emitter-collector path with one end coupled to said secondvoltage divider for responding to the potential developed thereby, asecond control transistor having a base coupled to the other end of saidemitter-collector path of said first control transistor and having anemitter-collector path coupled between said source of biasing potentialand said second dilferential amplifier, said first control transistorresponding to the potential difference across said first and secondvoltage dividers for being biased into conduction to in turn bias saidsecond control transistor into conduction to develop an overload signalfor disconnecting said regulating transistor in response to an overloadcurrent condition, said source of biasing potential maintaining saidoverload signal, and a leakage path across said regulating transistorfor passing current from said first and second voltage dividers torender them responsive for maintaining said control transistor biased inconduction during said overload condition.

References Cited in the iile of this patent UNITED STATES PATENTS825,023 Marantette Feb. 25, 1958 2,832,900 Ford Apr. 29, 1958 2,888,633Carter May 26, 1959 2,896,151 Zelinka July 21, 1959 2,904,742 ChaseSept. 15, 1959 2,915,693 Harrison Dec. 1, 1959 2,922,945 Norris et al Ian. 26, 1960 OTHER REFERENCES The Emitter-Coupled Dilerential Amplifier,Slaughter, IRE Transactions, March 1956, pp. 51-53.

Dodge: A Transistorized Overload-Proof Electronic Regulator, Transistorand Solid State Circuit Conference, Digest of Technical Papers, Feb. 2G,1958, pp. 35-36.

1. A VOLTAGE REGULATOR COMPRISING AN UNREGULATED SOURCE, A SERIESCIRCUIT INCLUDING A VARIABLE IMPEDANCE HAVING A TERMINAL FOR RESPONDINGTO A DISCONNECTING SIGNAL TO SUBSTANTIALLY PREVENT THE FLOW OF CURRENTTHERETHROUGH AND A LOAD COUPLED BETWEEN TERMINALS OF SAID SOURCE, MEANSCOUPLED ACROSS SAID LOAD TO DEVELOP A SIGNAL PROPORTIONAL TO MINORVARIATIONS IN POTENTIAL ACROSS SAID LOAD AND INCLUDING MEANS FORCOUPLING SAID PROPORTIONAL SIGNAL TO SAID VARIABLE IMPEDANCE TO CORRECTSAID MINOR VARIATIONS, OVERLOAD MEANS INCLUDING FIRST RESISTANCE MEANSCOUPLED IN SAID SERIES CIRCUIT FOR DEVELOPING A FIRST POTENTIAL AND ASECOND RESISTANCE MEANS COUPLED FROM BETWEEN SAID VARIABLE IMPEDANCE ANDSAID FIRST RESISTANCE MEANS ACROSS SAID LOAD FOR DEVELOPING A SECONDPOTENTIAL REPRESENTATIVE OF THE POTENTIAL ACROSS SAID LOAD AND INCLUDINGSWITCHING MEANS HAVING EITHER A CONDUCTIVE STATE OR A NONCONDUCTIVESTATE AND RESPONSIVE TO THE DIFFERENCE BETWEEN SAID FIRST AND SECONDPOTENTIALS DEVELOPED THROUGH SAID RESISTANCE MEANS AND COUPLED TO THETERMINAL OF SAID VARIABLE IMPEDANCE, SAID SWITCHING MEANS BEING BIASEDINTO A CONDUCTIVE STATE AND APPLYING A DISCONNECTING SIGNAL TO SAIDVARIABLE IMPEDANCE FOR EFFECTIVELY DISCONNECTING THE UNREGULATED SOURCEFROM SAID LOAD WHEN CURRENT THROUGH SAID LOAD EXCEEDS A PREDETERMINEDVALVE.